A common method for amplifying a sound of a stringed musical instrument, having one or more metal strings made by magnetic permeable material, uses a magnetic pickup positioned beneath the strings. When a person plays the stringed electric instrument, the stings vibrate with harmonic frequencies, which allows the pickup to sense vibration of the strings and generate an electric signal, which is then communicated to an amplifier and speaker system to generate a sound. Ideally, the sound will accurately reflect the vibration of the strings.
The pickup may include one or more coils wrapped around one or more magnetic permeable metal cores, which are themselves magnetic, or which are magnetised by an adjacent permanent magnet. The magnetic field created by this magnetic structure does not generate an electric signal inside the pickup metal coil by itself, because the magnetic field flow, flowing through the turns of the pickup coil, is constant (in absence of vibration of the strings).
Because the metal strings of the instrument are positioned near the magnetic structure of the pickup, a small area of each string becomes magnetised. This magnetised string area has a size close to the width of the exposed topside of the pickup magnet means.
In turn, the magnetised string area can radiate its own magnetic field toward the pickup. When the string is not vibrating, this magnetic field does not create an electrical signal inside the coil of the pickup. However, when the string does vibrate, for example, by being picked, strummed or bowed by a player of the instrument, the magnetised string area also vibrates and causes an alternating magnetic field to interact with the pickup, so as to cause an electric signal to pass through the coil.
The electric signal corresponds to the frequency of the strings mechanical vibration. The signal is passed through an electric circuit for amplification by an amplifier and through to a speaker system to create a human-audible sound.
Early pickup designs included a pickup designs included a pickup coil, wherein the coil was wound in a single direction, thus having a chiral characteristic. Such pickups are known in the technology as “single coil” pickups.
The term “chiral” is used in this specification and/or claims, and has its ordinary meaning, wherein an object that is chiral is not superposable onto its mirror image. A single coil winding, for example, is chiral because a right-handed wound coil is not similar to a left-handed wound coil, similarly, a clock wise wound coil is not similar to an anti-clockwise wound coil.
Whilst such single coil pickups are able to produce desirable tones, reflecting an accurate representation of the string vibrations, the single coil pickup design has a flaw, being that they are subject to also picking up much noise created by additional stimuli. These additional stimuli include external radio waves, electrical and magnetic disturbances created externally and also stimuli created within the circuitry of the electrical string instrument and/or amplifier, and other sources of electrical, magnetic or electromagnetic noise.
These additional stimuli are also detected by a pickup, which responds to the stimuli by producing noise signals within the pickup coil, similarly to the signals produced by the vibrating string or strings. The electrical signals generated in the coil by the additional stimuli may be referred to as noise signals, and the electrical signals generated in the pickup coil by the vibration of the string or strings may be referred to as musical signals.
Many different attempts have been made to solve the problem of the noise signals, which can cause unwanted distortion in the amplified sound of the stringed instrument. Previous solutions have attempted to, by various means, neutralise the noise signal, whilst preserving the musical signal. However, such previous solutions have caused secondary problems, such as alteration of the tone, timbre, or alteration of other qualities, of the musical signal, plus producing a sound which is considered not to have high fidelity.
A further problem with previous solutions is that they tend to increase output of a signal, and can therefore cause feedback problems.
Further, many, if not all of these previous noise reduction solutions have been complex, difficult and expensive to manufacture, difficult to operate and difficult to fit within the stringed musical instrument. Moreover, many, if not all of these previous noise reduction solutions are invasive to the musical instrument, which can result in a requirement to redesign the musical instrument before accommodation of such a device and its components. Furthermore, such invasive fitting or redesign of a musical instrument can result in an unpleasing aesthetic appearance, and reduction of the value of the instrument, particularly when the instrument is of great value and/or rarity.
One previous solution is described in U.S. Pat. No. 2,896,491 (S. E. LOVER). wherein a pickup 10 is provided, which is designed with two coils of wire 12, 14, wherein one coil is wound in an opposite direction to the other coil. This device also provides a bar magnet 16, which magnetises pickup magnets 18, located within their respective pickup coils 12, 14. One coil is induced by the bar magnet to have a north oriented magnetic field, the other coil is induced by the bar magnet to have a south oriented magnetic field. The coils are mounted next to each other and wired in series 24. A terminal 20 of one coil passes out to an amplification circuit, and carries the resultant signal. A terminal 22 from the other coil passes to ground.
The configuration depicted in FIG. 1 is designed to reduce noise by a 180° phase shift in the noise signal being introduced by one coil with respect to the noise signal introduced by the other coil. Unfortunately, the noise reduction device and method, as depicted in FIG. 1, also results in producing a different musical tone when compared with single coil pickups. Also, the pickup design shown in FIG. 1 has a wider magnetic field and is more complicated to manufacture than a single coil pickup. The altered tone of the musical signal emanating from such a double coil pickup is considered to be less desirable to some musicians and listeners.
FIG. 2 shows another previous solution, as disclosed in U.S. Pat. No. 6,291,759 (TURNER). This design again uses two pickups with coils wound in opposite directions (clockwise and anticlockwise), wherein one coil is stacked upon the other.
The device 30 includes coil A 32 which is wound clockwise and coil B 34, which is wound anticlockwise. The pickups include small cylindrical magnets 36. A terminal 38 from, coil A passes to signal, with another terminal 40 from coil B passing to ground. The coils 32, 34 are wired in series 42.
The solution depicted in FIG. 2, while producing a 180° phase reversal for noise cancellation or reduction, also produces a different tone, when compared with the tone produced by a single coil pickup. Similarly to the solution depicted in FIG. 1, the solution depicted in FIG. 2 is difficult to manufacture and requires un-aesthetic alteration of a musical stringed instrument. This may particularly be the situation where such a device is fitted as an after-market addition. Again, the resultant musical tone produced by the solution depicted in FIG. 2 is considered far less desirable by musicians and listeners, when compared with the tone produced by a single coil pickup.
A further previous solution was to include a “dummy coil”, introduced into the pickup circuit. Such a solution is depicted in FIG. 3, as disclosed in U.S. Pat. No. 5,569,872. The dummy coil 58 for this device 50 is mounted outside the magnetic field of the single coil pickup 52. The single coil pickup magnetic field being generated by pickup magnets 54. The dummy coil feeds a signal through terminal 64, along with the signal fed through the single coil pickup terminal 62, into a differential amplifier 60. Another terminal 56 of the pickup goes to ground.
This dummy coil may be of lesser impedance to the single coil pickup, and uses an active circuit in the differential amplifier (or transistorised circuit) to amplify the noise signal generated by the dummy coil to a level which is roughly equal to the noise generated by the single coil pickup. The device relies on the differential amplifier to produce a 180° phase shifted noise signal from the dummy coil with respect to the noise signal from the pickup.
Whilst the solution depicted in FIG. 3 retains the desired single coil pickup design, such solution introduces a bulky dummy coil and associated power supply and circuitry, which is complex, expensive and difficult to manufacture and it into a musical stringed instrument. Such a design also has the attendant undesirable result of an un-aesthetically pleasing musical instrument design. Moreover, the solution depicted in FIG. 3 also changes the tonal quality of the resultant musical signal, producing a sound which is less desirable for a musician and/or listener of the musical instrument.
A fourth variant noise reduction prior art solution is depicted in FIG. 4. This solution was disclosed in U.S. Pat. No. 7,259,318 (CHILIACHKI). This device introduces a large coil of wire of low impedance (approximately 200Ω to 1000Ω) a preferred embodiment of the CHILIACHKI device is an eight inch to sixteen inch coil, placed in a routed channel, machined into the stringed musical instrument body. This device 70 requires that the coil 74 is glued into the routed channel and shielded to ground 82.
As with the previously-described prior art device, this device uses a single coil pickup 72. which is magnetised by coil magnets 76. The pickup feeds a signal through terminal 80 and through another terminal 78 is connected to a control circuit,
One problem with the CHILIACHKI design is that the coil is required to be relatively large. which causes attendant problems with fitting such coil into a stringed musical instrument, where such stringed musical instrument does not necessarily have a large ready-made hollow area to contain such a large coil. As mentioned, in order to fit such a large coil, it is generally required to create a routed channel in the instrument. Of course, such routing is undesirable as it is expensive during manufacture, and can affect the tonal quality of the stringed musical instrument. Cutting such a channel into an instrument will also result in an aesthetically unpleasing appearance.
A further and very important disadvantage with the CHILIACHKI design is that it requires the large coil to be shielded from at least high frequency electromagnetic noise. Such shielding can be complicated to include with the instrument and such a noise reduction device, as well as adding expense to the manufacturer of the string instrument or the noise reduction device.
Moreover, the CHILIACHKI design requires connection to a control circuit containing resistors and capacitors. Again, where such extra circuitry must be used with such a noise reduction device, this adds expense to manufacture and such circuitry must also be placed somewhere within the stringed musical instrument, causing attendant manufacturing and aesthetic appearance problems.
It is an object of the present invention to overcome, or at least ameliorate, one or more of the above-mentioned problems in previous devices and methods. It is also another possible object of the invention to overcome, or at least ameliorate, other problems in the above-mentioned prior art, or other prior art, where such problems have not been mentioned above. Moreover, it is a further possible object of the invention to provide at least a useful alternative to previous devices and methods for noise reduction.
A possible application of the present invention is providing noise reduction of greater efficiency when compared with prior devices and/or methods, but without affecting musical qualities of an instrument, such as tone, timbre or other qualities.
Other possible applications of the present invention include providing a less-invasive, or non-invasive noise reduction device for fitting into a stringed electric instrument, either during manufacture or as a post-fitted, after-market device.
A further possible object includes providing an elegant and simple design, which may be low in cost and easy to fit.
Another possible application of the present invention is to provide a noise reduction device and/or method, which does not require replacement of existing single coil pickups.
Another possible application of the present invention is to provide a noise reduction device and/or method, which does not require placement near single coil pickups of an instrument.
It would be understood that the present invention is not to be limited by providing any one or more of the above-mentioned objects and/or applications, but that the present invention may be able to meet other objects and/or application, which have not been mentioned above.